This invention relates to a process for adapting slip control of an anti-skid brake system of automotive vehicles to the momentary friction coefficient or friction value between road surface and tires. The rotational behavior of the vehicle's wheels and the vehicular velocity of a derived value are measured. Braking force or braking pressure control signals are generated from the measured signals by means of logical combination and signal processing, upon the instabilization of a wheel, that is, upon the identification of a lock-up tendency. The braking force at the respective wheel is kept constant or reduced and reincreased at the appropriate time by means of said control signals. Processes with additional measurement of the braking force or of the braking pressure as well as circuit arrangements for carrying out the processes are also included.
A friction coefficient adapting circuit provided for anti-skid brake systems of automotive vehicles is kown. The circuit has several timing elements connected in series. One of the timing elements is energized when the skid threshold is reached, the following timing elements being energized as a function of reaching of the reacceleration threshold at the end of predetermined hold times (DE-PS=German Patent Specification No. 21 36 440). In this way only the pressure reduction phase is varied as a function of the reaccelerating behavior of the instabilized wheel.
Another known circuit for controlling the braking pressure in anti-skid brake systems of automotive vehicles in the initial phase is provided with a measuring device for the detection of the friction coefficient. By means of the device the time is measured which elapses between the end of a rotational acceleration signal and the occurrence of a rotational deceleration signal at the controlled wheel and is evaluated as a criterion of the friction value or friction coefficient (German Patent Specification=DE-PS No. 27 17 383). According to this known circuit, friction value adaptation only starts after the reacceleration and renewed deceleration or rather instabilization of the controlled wheel--i.e., at a relatively late moment.
It is thus an object of this invention to avoid the disadvantages of known circuits and to develop a process for adapting slip control to the respective road condition or rather to the adhesive value or friction value between road surface and tires which each time is achievable in order to effect an optimum slowing-down, said slip control starting immediately upon the occurrence of a first instability of a wheel (in case of an intact brake dimensioning this will be a front wheel) and favorably influencing the braking pressure variation in accordance with the friction value existent or detected, respectively.